The characteristics of geological formations surrounding a borehole are of significant interest in the exploration, production and monitoring of subsurface water and mineral deposits, such as oil and gas. A variety of techniques has been developed to measure and evaluate subsurface characteristics to determine certain characteristics of geological formations of interest.
These techniques typically include subsurface deployment of tools having energy sources to a radiated signal into the formations. The emitted energy interacts with the surrounding formations to produce signals that are detected and measured by one or more detectors also placed on the tool. The detected signal data are processed, and a log of the subsurface properties is transmitted to the surface.
A variety of logging techniques have been developed to evaluate subsurface formation by electromagnetically radiated waves, such as emission of neutrons into the formation, and e.g. evaluating the results of neutron interactions with the formation nuclei.
Properties of the geological formations which may be determined by means of radiation include formation density, porosity, carbon oxygen ratios, concentration of various chemical elements, properties of fluids and more.
Increased knowledge on the surroundings of the borehole leads to optimised drilling and production performance, thereby minimising costs and maximising return. During drilling and exploitation of a well, the well is typically continuously investigated further to reveal new possible branches of the well which might be exploited. The more detailed knowledge about the surroundings of the borehole that can be extracted from non-destructive measurements trough the casing of the borehole, the more the well can be investigated during operation without risking limitation in production time.
There is thus a need to be able to investigate the geological formation surrounding boreholes during exploration, production and monitoring of subsurface water and mineral deposits, such as oil and gas.